Male gerbils (Meriones unguiculatus) were bred and reared either grouped under enriched environmental conditions or isolated under impoverished environmental conditions. The objective of the present study was to examine the influence of social environment on structural and functional ontogeny of the medial prefrontal cortex (mPFC), In this respect, we investigated the maturation of both prefrontal dopamine (DA) innervation and working memory. For that purpose, at the age of postnatal day 90, prefrontal DA fibers were stained immunocytochemically using an antibody against glutaraldehyde-conjugated DA and innervation density was determined by means of a computer controlled program for image analysis. In order to evaluate environmental effects on working memory, 90-day-old gerbils were tested for y-maze delayed alternation, It was found that, isolation produced a significant and severe restraint of the maturation of prefrontal DA innervation, leading to fiber densities which were 56% below those in group-reared gerbils, Isolation also induced a significant impairment of delayed alternation performance on the y-maze indicating that obvious deficits in working memory had developed under restricted rearing conditions. The present results are discussed with regard to activity-dependent postnatal maturation of the cortex and adaptive neuroplasticity. (C) 1998 Wiley-Liss, Inc.